US 7442649 B2
A method for etching a dielectric layer over a substrate is provided. A photoresist mask is formed over the dielectric layer. The substrate is placed in a plasma processing chamber. An etchant gas comprising NF3 is provided into the plasma chamber. A plasma is formed from the NF3 gas. The dielectric layer is etched through the photoresist mask with the plasma from the NF3 gas.
1. A method for etching a low-k dielectric layer over a substrate, comprising:
forming a photoresist mask over the low-k dielectric layer;
placing the substrate in a plasma processing chamber:
providing an etchant gas consisting essentially of NF3 and an inert diluent into the plasma chamber;
forming a plasma from the etchant gas; and
etching the dielectric layer through the photoresist mask with the plasma from the etchant gas.
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7. A semiconductor device made by the method of
8. A method for etching a dielectric layer over a substrate comprising:
forming a photoresist mask no more than 400 nm thick over the dielectric layer;
placing the substrate in a plasma processing chamber;
providing an etchant gas consisting essentially of and a diluent into the plasma chamber;
forming a plasma from the NF3 gas; and
etching the dielectric layer through the photoresist mask with the plasma from the NF3 gas.
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The present invention relates to the use of a photoresist mask in semiconductor device production. More particularly, the present invention relates to etching a dielectric layer through a photoresist mask during the production of a semiconductor device.
During semiconductor wafer processing, features of the semiconductor device are defined in the wafer using well-known patterning and etching processes. In these processes, a photoresist (PR) material may be deposited on the wafer and then is exposed to light filtered by a reticle. The reticle may be a transparent plate that is patterned with exemplary feature geometries that block light from propagating through the reticle.
After passing through the reticle, the light contacts the surface of the photoresist material. The light changes the chemical composition of the photoresist material such that a developer can remove a portion of the photoresist material. In the case of positive photoresist materials, the exposed regions are removed, and in the case of negative photoresist materials, the unexposed regions are removed. Thereafter, the wafer is etched to remove the underlying material from the areas that are no longer protected by the photoresist material, and thereby produce the desired features in the wafer.
To provide increased density, feature size is reduced. This may be achieved by reducing the critical dimension (CD) of the features, which requires improved photoresist resolution. One way of improving photoresist resolution is by providing thinner photoresist masks.
New photoresist materials (193 and 157 nm PR) are being pursued to produce small CD sizes in the photoresist, but these resists are less resistant to damage from the plasma than previous masks of DUV and 248 nm photoresist. Also, with the current single layer approach, increasingly thinner resist must be used to match the resolution of the features. This may not provide enough resist for the dielectric etch and may cause other complications, such as striation, line edge roughness, and line wiggling. In order to keep up with shrinking feature dimensions, the industry has been investigating new technologies such as multi-layer approaches involving several processing steps. The switch to new technologies will undoubtedly be expensive and time-consuming.
In an effort to reduce the coupling capacitance levels in integrated circuits, the semiconductor industry has engaged in research to develop materials having a dielectric constant lower than that of SiO2, which materials are suitable for use in forming the dielectric layers in integrated circuits. A number of promising materials, which are sometimes referred to as “low-k materials”, have been developed. In the specification and claims, low-k materials are defined as materials with a dielectric constant k that is less than 4. Fluorosilicate glass is one example of a low-k dielectric, which has a dielectric constant of about 3.7. This composes an about 7-9% fluorine doped into SiO2.
There are several kinds of low-k materials currently being developed and in use in the semiconductor industry, i.e. fluorinated silicon oxyfluoride (FSG), hydrogen silsesquioxane (HSQ), spin-on organic materials (Dow's SiLK™ is a non-fluorinated, highly aromatic, organic spin-on polymer with a reported k of 2.65), and inorganic systems deposited by chemical vapor deposition (CVD) such as organosilicate glass. By way of example, but not limitation, such organosilicate dielectrics include CORAL™ from Novellus of San Jose, Calif.; Black Diamond™ from Applied Materials of Santa Clara, Calif.; Aurora™ available from ASM International N.V., The Netherlands; Sumika Film® available from Sumitomo Chemical America, Inc., Santa Clara, Calif., and HOSP™ from Allied Signal of Morristown, N.J. Organosilicate glass materials have carbon and hydrogen atoms incorporated into the silicon dioxide lattice which lowers the density, and hence the dielectric constant of the material. A dielectric constant for such films is typically <3.0.
To achieve the foregoing and in accordance with the purpose of the present invention a method for etching a dielectric layer over a substrate is provided. A photoresist mask is formed over the dielectric layer. The substrate is placed in a plasma processing chamber. An etchant gas comprising NF3 is provided into the plasma chamber. A plasma is formed from the NF3 gas. The dielectric layer is etched through the photoresist mask with the plasma from the NF3 gas.
In another manifestation a method for etching a dielectric layer over a substrate is provided. A photoresist mask no more than 400 nm thick is formed over the dielectric layer. The substrate is placed in a plasma processing chamber. An etchant gas consisting essentially of NF3 and a diluent is provided into the plasma chamber. A plasma is formed from the NF3 gas. The dielectric layer is etched through the photoresist mask with the plasma from the NF3 gas.
In another manifestation an apparatus for forming a features in an etch layer, wherein the layer is supported by a substrate and wherein the etch layer is covered by a photoresist mask is provided. A plasma processing chamber is provided. The plasma processing chamber comprises a chamber wall forming a plasma processing chamber enclosure, substrate support for supporting a substrate within the plasma processing chamber enclosure, a pressure regulator for regulating the pressure in the plasma processing chamber enclosure, at least one electrode for providing power to the plasma processing chamber enclosure for sustaining a plasma, a gas inlet for providing gas into the plasma processing chamber enclosure, and a gas outlet for exhausting gas from the plasma processing chamber enclosure. A gas source comprising an NF3 source is in fluid connection with the gas inlet. A controller is controllably connected to the gas source and the at least one electrode and comprises at least one processor and computer readable media. The computer readable media comprises computer readable code for providing NF3 gas from the NF3 source into the plasma processing chamber, computer readable code for generating a plasma from the NF3 gas, and computer readable code for providing plasma conditions to cause the etching of an etch layer with the plasma from the NF3 gas.
These and other features of the present invention will be described in more detail below in the detailed description of the invention and in conjunction with the following figures.
The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:
The present invention will now be described in detail with reference to a few preferred embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention.
To facilitate understanding,
To facilitate understanding of the invention,
CPU 822 is also coupled to a variety of input/output devices, such as display 804, keyboard 810, mouse 812, and speakers 830. In general, an input/output device may be any of: video displays, track balls, mice, keyboards, microphones, touch-sensitive displays, transducer card readers, magnetic or paper tape readers, tablets, styluses, voice or handwriting recognizers, biometrics readers, or other computers. CPU 822 optionally may be coupled to another computer or telecommunications network using network interface 840. With such a network interface, it is contemplated that the CPU might receive information from the network, or might output information to the network in the course of performing the above-described method steps. Furthermore, method embodiments of the present invention may execute solely upon CPU 822 or may execute over a network such as the Internet in conjunction with a remote CPU that shares a portion of the processing.
In addition, embodiments of the present invention further relate to computer storage products with a computer-readable medium that have computer code thereon for performing various computer-implemented operations. The media and computer code may be those specially designed and constructed for the purposes of the present invention, or they may be of the kind well known and available to those having skill in the computer software arts. Examples of computer-readable media include, but are not limited to: magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD-ROMs and holographic devices; magneto-optical media such as floptical disks; and hardware devices that are specially configured to store and execute program code, such as application-specific integrated circuits (ASICs), programmable logic devices (PLDs) and ROM and RAM devices. Examples of computer code include machine code, such as produced by a compiler, and files containing higher level code that are executed by a computer using an interpreter. Computer readable media may also be computer code transmitted by a computer data signal embodied in a carrier wave and representing a sequence of instructions that are executable by a processor.
An etchant gas comprising NF3 is provided to the plasma chamber 300 (step 116). In an example, the etchant gas comprises NF3 and an inert gas, such as Ar. For example, the etchant gas may be 60 sccm NF3 and 100 sccm Ar. As in this example, preferably, the etchant gas is free of fluorocarbons and hydrofluorocarbons.
The etchant gas is converted to a plasma (step 120). In this example the pressure in the plasma chamber is set at 120 mTorr. The RF source provides 500 Watts at 27 MHz and 100 Watts at 2 MHz. The plasma from the etchant gas is used to etch features 232 into the dielectric layer 220, as shown in
The invention may be used to etch a variety of dielectric materials. The invention may be used to etch silicon oxide based dielectric materials, such as silicon oxide and organo silicate glass. In another manifestation of the invention, the invention may be used to etch low-k dielectrics, which may be either organic based or silicon oxide based. Examples of organic based low-k dielectrics that may be etched by the invention are SiLk and organo silicate glass.
Preferably, the invention uses a photoresist of 193 nm or above. Such photoresists tend to have a low carbon to hydrogen ratio (C/H ratio) and are less etch resistant.
Photoresist selectivity is defined by the etch rate of the dielectric layer divided by the etch rate of the photoresist. Generally, photoresist selectivity may be increased by lowering the photoresist etch rate. The inventive NF3 etch is believed to increase the photoresist etch rate, but increases photoresist selectivity by increasing the dielectric etch rate more than the increase in the photoresist etch rate.
Conventional etches would lower photoresist etch rate by depositing carbon or polymer on the photoresist before or during the etch. Such processes would cause microloading between patterns. Such microloading would cause uneven etching between areas with closely spaced features and areas with more distantly spaced features.
The inventive process using only an NF3 etchant with no hydrocarbon, fluorocarbon, or hydrofluorocarbon component does not seem to deposit carbon or polymer and therefore does not cause microloading.
In addition, the inventive process may reduce or eliminate photoresist wiggling. Photoresist wiggling is caused by a distortion or bending of the photoresist mask material. The bent or distorted photoresist mask causes irregularly shaped features. It is believed that such distortion or bending of the photoresist mask material is caused by protective layers, hydrofluorocarbon polymer, put on the photoresist mask to reduce the photoresist etch rate. Such protective layers of carbon or polymer apply a force to the photoresist mask, which causes the photoresist mask to bend or distort.
This process may be used to reduce line edge roughness and striation, since line edge roughness and striation is generally cased by uneven polymer deposition on during etch process.
While this invention has been described in terms of several preferred embodiments, there are alterations, permutations, modifications, and various substitute equivalents, which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and various substitute equivalents as fall within the true spirit and scope of the present invention.